The present invention relates to tightening tools for use in cases involving the problem of over-tightening or undertightening as in tightening up pipe joints.
The production equipment of the chemical industry and semiconductor industry includes piping systems for transporting or controlling fluids and maintaining or controlling a vacuum. Joints are generally used for connecting pipes together and for connecting a pipe to a valve, flow meter or like instrument, or reactor. High gastightness, corrosion resistance to fluid substance and a superhigh degree of cleanliness with the utmost freedom from dust are required of the piping system especially in the semiconductor industry. For example, FIG. 8 shows a joint which is used as the most suitable one from this viewpoint.
With reference to the drawing, a first joint member 21 and a second joint member 22 are butted against each other with an annular gasket 23 interposed therebetween, and the first joint member 21 is fastened to the second joint member 22 with a nut 24 provided on the second member 22 and screwed on the first member 21. A pipe 25 is inserted in the second joint member 22 from the other end thereof and fixed to the second member 22 at a welded portion 26. Gasket holding annular ridges 27, 28 are formed on the butting ends of the first and second joint members 21, 22, respectively, The gasket 23 is held to the end of the first joint member 21 by a retainer 29.
With the pipe joint described, it is not desirable that the nut tightening torque be too small or too great. If the torgue is too small, gastightness is not available, while too great a torque will excessively deform or break the gasket 23 to result in creation of dust or lower corrosion resistance, consequently leading to impaired gastightness. Thus, it is important that the nut 24 be tightened up with an appropriate torque. This is also true of the case wherein a metal ring, such as an O-ring or ferrule, is provided between the butting ends of the first and second joint members 21, 22 in place of the gasket
A spanner is usually used for tightening up such a joint. The joint is tightened up suitably by manually tightening up the nut 24 on the first joint member 21, making a mark on each of the member 21 and the nut 24 in this state and thereafter rotating the nut with the spanner through a required angle (e,g., 1/4 of a turn) with reference to the marks.
The use of the spanner as a tightening tool thus necessitates the procedure of making a mark on each of the first joint member and the nut as tightened up thereon by hand and thereafter rotating the nut with the spanner through the required angle while visually recognizing the marks. However, this procedure needs labor, depends largely on intuition and has the problem of low reliability, for example, because the manual tightening force differs from person to person or varies according to the mood of the moment,
A device therefore appears useful which is adapted to tighten up the nut white detecting the tightening torque and determining whether the detected torque is proper, but such a device will be a great one and inferior to the conventional tool in respect of the manufacturing cost and easiness of use.